Negative resistance



A. W. HULL.

NEGATIVE RESISTANCE.

APPLICATION FILED Aue.30, 1915.

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ALBERT W. HULL, 01

UNITED STATES PATENT OFFICE.

SCHENECTADY, NEW YORK, ASSINOR '10 COMPANY, A CORPORATION OF NEW YORK.

GENERAI, anaemic NEGATIVE nnsrs'rmcn.

Specification of Letters Patent. Patented A 1921.

Application an August so, 1915. Serial No. 47,988.

To allwhom z't may concern:

Be it known that I, ALBERT W. HULL, a

citizen of the United States, residing at Schenectady, county of Schenectady, State.

provide a devicehaving negative electrical resistance characteristics; that is, a device in which the current will decrease as the potential applied thereto increases in contradistinction to theordinary resistance devices in which an increase of potential is accompanied by an increase in current.

The novel features of my invention I have pointed out with particularity in the appended claims, the invention itself, however, both as to its construction and method of operation, Will best be understood by reference to the following description taken in connection with the accompanying drawing, in which Figure '1 shows a device which may be utilized in carrying my invention into effect; Fig. 2 shows the application of my invention for the amplification of variable potentials; Fig. 3 shows a wireless receiving system in which a negative resistance is utilized, and Fig. 4 shows the current characteristics of one of my devices.

The device shown in Fig. 1 consists of a highly evacuated envelop 1 provided with a filamentary cathode 2 connected to leading-in conductors 3 for-supplying current for heating it to incandescence. This cathode is preferably surrounded by a helical wire grid 4 which serves as an anode and which is connected to a leading-in wire 5. Surrounding the cathode and'anode is a third electrode consisting of a metal cylinder 6 connected to a leading-in wire 7. This cylinder is preferably fairly close to the anode though the relative positions of the three electrodes may be varied in order to vary the operating characteristics of the device. The envelop 1 should preferably be exhausted to such a degree of vacuum that when potentials of the magnitude desired for operation are applied to the electrodes there will be no visible manifestations of gas ionization such as blue glow.

If the cathode is connected to earth and heated to incandescence and a positive po tential impressed upon the anode, there will be a flow of electrons from cathode to anode.

If the third electrode is also at earth potential, no, electrons will be received thereby because it is at the same potential as the cathode. If. however, a small positive potential. is applied to the third electrode,'a portion of the electrons which pass through the grid anode will strike it and it will recelve a current of negative electricity. The velocity with which these electrons will strike the third electrode will depend upon the potential difierence between it and the cathode. If this potential is increased, the

velocity' will increase until the electrons striking the third electrode are able, by their impact, to liberate secondary electrons. These secondary electrons leaving the third electrode will be attracted to the morepositive anode. As the potential is increased, a point will finally be reached at which the number of secondary electrons leaving the third electrode is just equal to the. number of primary electrons that strike it, that is each electron that strikes liberates on the average one secondary electron. No current Will then be received by the third electrode. If the potential of the third electrode is further increased, the number of seconda electrons given off becomes greater than the number of primary electrons received and as a result the third electrode loses elec-- trons, thereby supplying current to the anode instead of receiving current. 5

These characteristics can best be understood by reference to the curve shown in Fig. 4, in which the ordinates represent the electron current flowing to or away from the third electrode and the absicissae represent the potential of the third electrode. The part A B- represents the increasing electron current reaching the .third electrode as the potential is increased-.' When the potential of the third electrode increases beyond that corresponding to the point B, the rate of increase in the emission of secondary electrons exceeds the rate of increase in primary elec trons received and the current begins to decrease. When the potential of the third elec: trode reaches the point D, it loses as many electrons as it receives, and the current becomes zero. From D to E the number of secondary electrons given oif continues to increase and the electron current from the third electrode to theanode increases. The point E is finally reached, however, at which Y the potential of the third electrode so closely approaches that of the anode that the number of secondary electrons lost by the third electrode begins to decrease because of the fact that the difference of potential between anode and third electrode is not great enough to attract as many electrons to the anode as before. This continues until the point F is reached, where the number of secondary electrons which leave the third electrode and do not return is equal to the number of primary electrons which strike it, and the current again becomes zero. From this point the electron current received by the third electrode increases with increase in its potential.

is positive or negative. R corresponds to the resistance of an ordinary circuit except that in this case it is a negativeresistance. Thus it will be seen that there is a certain range through which the device may be operated in which the current receivedby the third electrode will decrease as the potential applied thereto increases. In the description which follows and in the claims the term negative resistance) is used to designate a device havingnegative resistance characteristics.

It is not at all essential in the operation of my device that the portion B E of the current curve should extend below the axis and in case it does extend below the axis, as in the example given, it is immaterial'whethcr the normal electron current comes upon the portion B D or the portion D E of the curve.

In Fig. 2 I have illustrated a system in which a negative resistance device such as I have described above may be utilized to ampilfy potential variations. The negative resistance 8 here indicated is constructed as shown in Fig. 1. A battery 9 provides current for heating the filamentary cathode 2 and battery 10 is employed to impress a constant positive potential upon the anode 4. A battery 11 is also employed with a resistance 12 in series therewith to impress a positive potential upon the third electrode of such a value that the device will operate at a point on the portion B E of the current curve. Transformer 13, the primary winding of which is connected to the source of potential variations which it is desired to amplify, will impress a variable potential upon the circuit. When the connections are made in this way and no potential is supplied by the transformer 13, a certain definite current will flow in the circuit. When current is flowing there will be a drop of potential through the resistance 12 and the difference of potential between the cathode and the third electrode will be equal to the difference between this drop and the potential of battery .11. If the resistance 12 is greater than the constant B of the negative resistance and 'if the additional potential supplied by transformer 13 is in the same direction as that supplied by battery 11, the first effect of the additional potential will be to increase the drop in potential through resistance 12 and cause the third electrode to become less positive with respect to the cathode. As. a result more current will flow in the circuit. With more current flowing the drop across resistance 12 increases ancl the third electrode becomes still less positive causinga further increase in the current. When a point has finally been reached at which the current becomes stable the change in the potential difference across the resistance will be much greater thanthe potential applied by transformer 13.- The degree of amplification or the rate ofchange in potential across the resistance 12 with changes in the potential applied to the circuit depends upon the ratio of resistance 12 to the difference between resistance 12 and the constant B. The closer these are to each other in value the greater will be the degree of amplification. If the resistance 12 is less than the constant R the same will hold true and the action will be like that just described, but the effect of the additional p otential will be to decrease the drop through resistance 12 and decrease the current flow. WVhile in the above explanation the current has been considered as reaching its stable value by a series of gradations, it actually reaches that value immediately and responds to all voltage variations no matter how short their duration. If the extra potential'supplied by transformer 13 is in the opposite direction to that of battery 11 the action will be just the reverse of that above 'may equally well. be any other device possessing positive resistance characteristics.

'In Fig. 3 I have illustrated the use of a -described, that is when resistance 12 is p negative resistance device to increase the degree of amplification of a Wireless receiving system. The receivingsystem here shown comprises an antenna 14 which is coupled by means of transformer 15 to the grid circuit of an electron discharge amplifier 16. This device comprises a filamentary'cathode 17, a coeperating anode 18 and an interposed discharge controlling grid '19 inclosed in a highly evacuated envelop. The operation of. devices of this nature is too well known to require further explanation. The plate circuit of. this amplifier is supplied with current by the portion 20 of battery 21 and includes a resistance 22 which v.is' connected in'the grid circuit of a seconil amplifier 23 similar in structure to the first. The plate circuit of this amplifier which includes the telephone receiver 24 is supplied by the portion 25 of battery 21. Negative resist ance device 26 has its anode 27 supplied with a constant positive potential by battery 21 and its third electrode 28 connected to one terminal of resistance 22. I

When signals are received by the antenna 14 the. potential of grid 19 is varied and the current flowing in the plate circuit of amplifier 16 Varies accordingly. If for the moment the efi'ect of the negative resistance is neglected these changes in current willproduce corresponding potential variations across the terminals of resistance 22 and thus vary the potential of the grid of amplifier 23 and cause a' corresponding'variation in the current through the telephone receiver 24. The current flowing in the plate circuit of amplifier 16 depends upon the potential of grid 19 andxupon the difierence of potential between its electrodes. As, the current through resistance 22 increases the drop of potential therethrough increases and the difference of potential between the electrodes of amplifier 16 decreases. Hence the current flowing through amplifier 16 will not increase to the value which it would reach it this potential remained constant. This effect however is compensated for by the negative resistance which acts in'this respect in a manner directly opposite to that of the amplifier. The negative resistance in this case is in parallel to the positive resistance and it is therefore evident that potential variations between the terminals of positive resistance 22 and negative resistance 26 will be exactly equal to the potential variations.

between the cathode and anode of-amplifier 16 only in the reverse direction. The effect of these potential variations upon the two resistances is not the same, however. The change in this potential which is-applied to the two resistances will produce 'a change in current in one direction in the negative resistance and in the opposite direction in the positive resistance. Hence, it will be apparent that the effect of applying the potential mentioned to the two resistances will be to produce a current which circulates between the two resistances and which does not flow through amplifier 16. The currents through the two resistances, howbe merely the current which circulates between the two resistances and does not pass through amplifier 16. As a result, the cur-,. rent in resistance 22 may be much greater than that. flowing through amplifier 16 and the potential variations across resistance 22 will be greater than the potential variation which can be produced by amplifier 16 alone. In other words the. amplification may be made much greater than would be possible without the negative resistance. In practice it will be found that the best results are obtained when the negative resistance is given such a value as to compensate as closely as possible for the resistance both of the amplifier 16 and the resistance 22.

I have indicated a convenient construction for my negative resistance in Fig. 1, but many variations therein may be. made without changing the principle of its operation. In general the third electrode should be placednear the anode and in such position that some ofthe electrons from the cathode will strike it even when it is less positive inpotential than the anode; and the relative positions should also be such that secondary electrons given off by the third electrode can readily reach the anode.

In the above. description and in the claims which follow I have used'such expressions ascurrent flow from cathode to third electrode to designate the net electron current received by the third electrode, or the current which will flow in the external circuit between cathode and third electrode.

What I claim as new and desire to secure by Letters Patent of the United States, is:

' 1. A negative resistance device comprising a plurality of electrodesinclosed in a highly evacuated receptacle and having sources of potential applied to said electrodes in such a way that the device has'a working range over which the current flow between two of said electrodes increases and decreases inversely as the potential appliedbetween said two electrodes.

A negative resistance device comprising an electron emitting cathode adapted to be heated to incandescence independently of the current passing through the device and electrodes cooperating therewith and having sources ot potential supplied to said electrodes in such a Way that the device has a working range over which the current flow '5 3. A negative resistance device comprising an electron emitting cathode-an anode and a third electrode inclosed in a highly evacuated envelop and having sources of potential. applied to said electrodes in such a way that the device has a worklng range over which the current flow from the cathode to-the third electrode varies inversely asthe' potential applied thereto.

4. i In combination, a device compris ng an electron emitting cathode, an" anode and a third electrode and sources'of potential applied to said electrodes 1n such a way that the device has a working range over which the current flow from the cathode to the third electrode varies inversely as the potential applied thereto, said third electrode being located near the anode and so positioned with respect to the cathode and anode that itwill receive electrons from the cathode when it is more positive than the cathode, and that secondary electrons given 011' from the third electrode can readily reach the anode.

5. In combination, a devicecomprising an electron emitting cathode, an anode, and a third electrode, said third electrode beinglocatednear the anode and so positioned with respect to the cathode and anode that it will receive electrons from the cathode when it is more positive than the cathode, and that secondary electrons given ofi from the third electrode can readily reach the anode and sources of potential applied to said electrodes of suchvalue that the number of elec- -trons received and retained by the third electrode over a iven working range will vary inversely as t e potential applied thereto.

6. A negative resistance device comprising an electron emitting cathode, an anode and a third electrode, said anode being interposed .between cathode and third electrode and having openings therein through which electrons can reach the third electrode when it is more positive than the cathode, and sources of potential applied to said electrodes of such value that the number of electrons received and retained by the third electrode over a given working range will vary inversely as t e potential applied thereto.

7. The combination of a negative resistance device comprising an electron emittin cathode, an anode and a third electrode inc osed in an evacuated envelop, means for directly producing by impact an emission of secondary electrons from said third electrode and means for varying the secondary electron emission from said third electrode, the envelop being exhausted to such a degree that with the, potentials necessary for producing the secondary electron emission applied to the electrodes the device Will operate without any appreciable gas ionization.

8. The combination of a negative resistance device comprising an electron emitting cathode, ail-anode and a third electrode inclosed in an evacuated envelop, means for impressing constant positive potential upon the anode, means for directly producing by impact .an emission of secondary electrons from the third electrode, and means for varying the secondary electron emission v from said third electrode, the envelop being exhausted to such a degree that with the potentials necessary for producing the secondary electron emission applied to the electrodes the device will operate without any appreciable gas ionization. p

9. The combination of a negative resistance device comprising an electron emitting cathode, an anode and a third electrode inclosed in an evacuated envelop, means for impressing a constant positive potential upon said anode, means for impressing a positive potential upon the third electrode of such a value as to directly produce by inipact an emission of secondary electrons from said electrode, and means for impressing a variable potential upon said third electrode to vary the secondary electron emission therefrom, the envelop being exhausted to such a degree that with the potentials necessary for producing the secondary electron emission applied to the electrodes the device will operate without any appreciable gas ionization.

10. The combination of an electron discharge device comprising a cathode, an anode and a third electrode inclosed in a highly evacuated envelop, means for impressing a definite potential upon the anode and means forimpressing a variable potential upon the third electrode, the electrodes being so proportioned and related to each other that the current to the third electrode varies inversely as the potential applied thereto over a given working range.

11. Means for amplifying potential variations comprising a positive resistance and a negative resistance device in series therewith, thetwo resistances being approximately equal to each other in value, said negative resistance device comprising an electron emitting cathode and cooperating electrodes in an evacuated receptacle, and being operable as a negative resistance by electron currents independently of any appreciable gas ionization.

12. Means for amplifying potential variations comprising a device having positive resistance characteristics, and a negative resistance device in series therewith, the resistance of the two devices being approximately equal to each other in value, said negative resistance device comprising an electron emitting cathode and cooperatin electrodes in an evacuated receptacle, and eing operable as a negative resistance by electron currents independently of any appreciable gas ionization.

13. Means for amplifying potential variations comprising a positive resistance, a negative resistance device of substantially the same value in series therewith, and means for supplying a constant potentialto said resistances, said negative resistance device comprising anelectron emitting cathode and cooperating electrodes in an evacuated receptacle and being operable as a negative resistance by electron currents independently of any appreciable gas ionization.

14:. Means foramplifying potential variations comprising a negative resistance device, a positive resistance of substantially the same value, and means for supplying the potential variations which are to be amplified to the two resistances in series, said negative resistance device comprising an electron emitting cathode and cooperating electrodes in an evacuated receptacle and being operable as a negative resistance by electron currents independently of any appreciable gas ionization.

15. Means for amplifyingpotential variations comprising a negative resistance device, a positive resistance, means for supplying a constant potential to said resistance in serles and means for supplying the potential variations which are to be amplified to the two resistances in series, said negative resistance device comprising an electron emitting cathode and cooperating electrodes -in an evacuated receptacle and being'operable as a negative resistance by electron currents independently of any appreciable gas ionization.

16. Means for amplifying potential variations comprising a negative resistance device having a working range over which the current flow therethrough increases and decreases inversely as the potential applied thereto, a positive resistance of a value substantially equal to that of the negative resistance device and means for supplying the potential variations which are to be amplified to the two resistances in series, said negative resistance device comprising an electron emitting cathode and cooperating electrodes in an evacuated receptacle and being operable as a negative resistance by electron currents independently of any appreciable gas ionization; 1

17. Means for amplifying potential variations comprising a negative resistance device comprising an electron emitting cathode and cooperating electrodes in an evacuated receptacle and operable as a negative resistance by electron currents independently of any appreciable gas ionization and ations which are to be amplified to the two resistances in series.

18. Means for amplifying potential variations comprising a negative resistance device having an electron emitting cathode and having a working range over which the current flow therethrough varies inversely as the potential applied thereto, said device comprlsing an electron emitting cathode and cooperating electrodes in an evacuated receptacle and being operable over such a range by means of electron currents independently of gas ionization, a positive resistance of a value substantially equal to that of the negative resistance device and means for supplying the potential variations which are to be amplifiedto the two resistances in series.

19. Means for amplifying potential variations comprising a negative resistance having an electron emitting cathode, an anode, and a third electrode inclosed in a highly evacuated envelop and having a working range over which the current flow from the cathode to the third electrode varies inversely as the potential applied thereto, a positive resistance having a value substantially equal to that of the negative resistance and means for supplying the potential variations which are to be amplifiedto the two resistances in series.

20. Means for amplifying potential variations comprising a negative resistance having an electron emitting cathode, an anode and a third electrode inclosed in a highly evacuated envelop and havin a working range over which the current ow from the cathode to the third electrode varies inversely as the potential applied thereto, a positive resistance havin a value substantially equal to that of t e negative resistance, means for supplying a constant potential to said resistances in series, and means for supplying the potential variations which are to be amplified to the two resistances in series.

21. Means for amplifying potential variations comprising a negative resistance having an electron emitting cathode, an anode and a third electrode near the anode and so positioned with respect to the cathode and anode that it will receive electrons from the cathode when it is more positive than the cathode and that secondary electrons given oif from the third electrode can readily reach the anode, a positive resistance and means for supplying the potential variations which are to be ampllfied to the'two resistances in series.

22. Means for amplifying potential var ations comprising a negative resistance device comprising an electron emitting cathode and cooperating electrodes in an evacuated receptacle and being operable as a negative resistance by electron currents independently of any appreciable gas ionizat'ion, a positive resistance and means for supplying potential variations which are to be amplified to the two resistances in series, the two resistances being approximately equal to each other in value.

23. Means for amplifying potential variations comprising an electron discharge device having an electron emitting cathode, an anode and a third electrode, means for directly producing by impact an effective emission of secondary electrons from said third electrode and means for varying, the secondary electron emission from said third electrode.

24. Means for amplifying potential variations comprising a device having positive resistance characteristics, a negative resistance and a positive resistance in series with said device and said negative reslstance, said negative resistance having such a value as to compensate as closely as possible 'for theother resistance in the circuit.

25. Means for amplifying potential variations comprising an electron discharge amplifier, a negative resistance and a positive resistance in series with said amplifier and said negative resistance, said negative resistance having such a value as to compensate as closely as possible for the resistance of the amplifier and the positive resistance.

26. The combination in a wireless signaling system of a negative resistance and a device having positive resistance characteristics in series therewith, said negative resistance having such a value as to compensate as closely as possible for the positive resistance in the circuit.

27. The combination in a wireless receiving system of a device having positive reand a positive resistance in series with said device and said negative resistance, satid.

negative resistance having such a value as to compensate as closely as possible for'the positive resistance of the circuit.

28. The combination in a wireless receiving system of an electron discharge amplifier, a negative resistance and a positive resistance in series with said amplifier and said negative resistance, said negative resistance having such a value as to compensate as closely as possible for the positive resistance of the circuit.

29. A negative resistance device comprising an electron emitting cathode, an anode and a third electrode inclosed'in an envelop evacuated to such a degree that with anyoperating potentials which may be applied to the electrodes the device will operate inderange over which the current flow between cathode and third electrode varies inversely as the potential applied between said cathode and'third electrode.

30. The method of operating an electron discharge device comprising an electron emitting cathode, an anode and a third electrode which consists in producing an emission of secondary electrons from the third electrode sufiicient to give the device a nega tive resistance characteristic and applying a variable potential to said third electrode to vary the number of secondary electrons emitted therefrom.

31. The method of operating an electron discharge device comprising an electron emitting cathode, an anode and a third electrode which consists in applying a constant positive potential to the anode and applying a positive potential to the third electrode of such a value as to produce an emission of secondary electrons therefrom sufficient to give the device a negative resistance characteristic.

32. The method of operating an electron discharge device comprising an electron emitting cathode, an anode, and a third electrode which consists in applying a 'constant potential to the anode, ap lying a smaller positive potential to the third electrode to produce an emission of secondary electrons therefrom and varying the positive potential of the third electrode to vary the secondary electron emission.

33. The method of operating an electron discharge device comprising an electron emitting cathode, an anode and a third electrode which 'consists in applying constant positive potential to the'anode and applying a positive potential to the third electrode of such a value as to give the device a I negative resistance characteristic. sistance characteristics, a negatlve resistance thode and two cooperating electrodes and means for directly producing byim act an efiective emiss on of secondary e ectrons from one of saidcooperating electrodes by reason of a bombardment thereof by a stream of primary electrons emanating from the cathode.

36. A thermionic amplifier having a cathode and two cooperating electrodes and means for directly producing by impact an efiective emission of secondary electrons from one of said cooperating electrodes by reason of a bombardment thereof by an electronic stream emanating from the cathode.

37 An electron discharge device comprising a cathode, an anode and a third electrode, and means for maintaining the anode and third electrodes at difierent potentials 15 with respect to the cathode, said third electrode being. rendered electronically activeand third electrode at difierent potentials with respect to the cathode, said third electrode being rendered electronically active by bombardment by a thermionic stream emanating from the cathode.

In witness whereof, I have hereunto set my hand this 28th day of August, 1915.

ALBERT W. HULL. 

